1. Field of the Invention
This invention relates to large material handling systems; more particularly, it relates to a means for extending and retracting a crane boom assembly mounted on a superstructure of a mobile crane.
A large mobile crane of the type with which the present invention is concerned typically includes a telescoping boom assembly having two or more extensible and retractable boom sections nested within a non-extensible boom base section which is pivotally mounted on the superstructure of the crane. In operation, the boom assembly is mounted on the superstructure for rotation about a horizontal axis and may be rotated to lock at a potentially infinite number of inclined working positions which range from 0.degree. to 80.degree. C with respect to the horizontal. The amount of extension of the boom assembly and the angle of inclination determine the height between which loads may be raised or lowered by the boom assembly. Typically, the boom assembly operates with the telescoping sections fully extended to increase the working height of the boom.
2. Known Systems
The boom assembly is generally extended and can be retracted by linear motors or hydraulic cylinders operatively connected between adjacent sections of the telescoping boom assembly.
For example, many boom extension and retraction means require that a linear motor be placed between each adjacent pair of telescoping boom sections to insure full extension of the boom assembly. This requirement adds substantial weight to the completed boom assembly, thus greatly increasing the bending stresses acting on the boom assembly, and severely reducing the overall operating capacity of the crane.
Those few systems which use a single fluid driven cylinder to extend a plurality of telescoping boom sections, must be vertically oriented for extension, retraction and operation of its boom assembly. For example, a tower crane operates at substantially lower load levels and smaller operating radii than the cranes of the present invention. Bending loads on the tower itself are minimal and the cylinder does not contribute significantly to stresses exerted on the crane. Consequently, the weight of the hydraulic cylinder is not an important consideration in the design of tower cranes. Futher, such known boom assemblies provide substantial overlap between adjacent telescoping sections.
Latch mechanisms for an extensible crane boom assembly can range from the very unsophisticated to the relatively complex and can include latching means at both top and bottom of each interconnected telescoping section.
Means and apparatus for extending and retracting the telescoping boom assembly of a mobile crane should comprise a single lightweight cylinder to minimize the bending stresses exerted on the boom assembly by the extension and retraction apparatus and should include a latch mechanism having positive locking for the extended boom sections of the boom assembly, permitting selective extension of various of the sections of the boom assembly, providing guide means for the extension and retraction apparatus of the boom assembly to insure the reliability of the locking means for the extension and retraction apparatus, the mechanism comprising single latching means and utilizing a minimum number of operating parts.
The object of the present invention is to provide an improved apparatus for the extension and retraction of the telescoping boom assembly of a mobile material handling crane wherein the apparatus permits extension and retraction at any angular displacement of the boom assembly and a single fluid driven power cylinder may be used to selectively extend and retract the plurality of telescoping boom sections of the boom assembly.
A further object of the present invention is to provide an improved single latch mechanism including first means for engagement and disengagement of the locking means associated with each of the boom sections of the boom assembly and second means for extension and retraction of the boom assembly, both means being commonly aligned on the latch mechanism.
Another object of the present invention is to provide positive locking means between adjacent sections of the telescoping boom assembly.
Another object of the present invention is to provide guide means associated with the fluid driven power cylinder to insure that the positive locking means are properly aligned with the boom sections of the telescoping boom assembly to insure positive locking between adjacent sections of the boom assembly.